<meta charset="utf-8">
(#) You must call collect on the given progress flow when using PredictiveBackHandler

!!! ERROR: You must call collect on the given progress flow when using PredictiveBackHandler
   This is an error.

Id
:   `NoCollectCallFound`
Summary
:   You must call collect on the given progress flow when using PredictiveBackHandler
Severity
:   Error
Category
:   Correctness
Platform
:   Any
Vendor
:   Jetpack Activity Compose
Identifier
:   androidx.activity.compose
Feedback
:   https://issuetracker.google.com/issues/new?component=612128
Min
:   Lint 8.0 and 8.1
Compiled
:   Lint 8.0 and 8.1
Artifact
:   [androidx.activity:activity-compose](androidx_activity_activity-compose.md.html)
Since
:   1.8.0
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/activity/activity-compose-lint/src/main/java/androidx/activity/compose/lint/CollectProgressDetector.kt)
Tests
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/activity/activity-compose-lint/src/test/java/androidx/activity/compose/lint/CollectProgressDetectorTest.kt)
Copyright Year
:   2023

You must call collect on the progress in the onBack function. The
collect call is what properly splits the callback so it knows what to do
when the back gestures is started vs when it is completed. Failing to
call collect will cause all code in the block to run when the gesture is
started.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/com/example/test.kt:9:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:13:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:17:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:26:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:29:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:35:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
src/com/example/test.kt:39:Error: You must call collect() on Flow
progress [NoCollectCallFound]
    PredictiveBackHandler { progress -&gt; }
                            --------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/com/example/test.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package com.example

import androidx.compose.runtime.Composable
import androidx.activity.compose.PredictiveBackHandler

@Composable
fun Test() {
    PredictiveBackHandler { progress -> }
}

val lambda = @Composable {
    PredictiveBackHandler { progress -> }
}

val lambda2: @Composable () -> Unit = {
    PredictiveBackHandler { progress -> }
}

@Composable
fun LambdaParameter(content: @Composable () -> Unit) {}

@Composable
fun Test2() {
    LambdaParameter(content = {
        PredictiveBackHandler { progress -> }
    })
    LambdaParameter {
        PredictiveBackHandler { progress -> }
    }
}

fun test3() {
    val localLambda1 = @Composable {
        PredictiveBackHandler { progress -> }
    }

    val localLambda2: @Composable () -> Unit = {
        PredictiveBackHandler { progress -> }
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/activity/activity-compose-lint/src/test/java/androidx/activity/compose/lint/CollectProgressDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `CollectProgressDetector.errors`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=612128.

(##) Including

!!!
   This is not a built-in check. To include it, add the below dependency
   to your project.

```
// build.gradle.kts
implementation("androidx.activity:activity-compose:1.10.0-rc01")

// build.gradle
implementation 'androidx.activity:activity-compose:1.10.0-rc01'

// build.gradle.kts with version catalogs:
implementation(libs.activity.compose)

# libs.versions.toml
[versions]
activity-compose = "1.10.0-rc01"
[libraries]
# For clarity and text wrapping purposes the following declaration is
# shown split up across lines, but in TOML it needs to be on a single
# line (see https://github.com/toml-lang/toml/issues/516) so adjust
# when pasting into libs.versions.toml:
activity-compose = {
    module = "androidx.activity:activity-compose",
    version.ref = "activity-compose"
}
```

1.10.0-rc01 is the version this documentation was generated from;
there may be newer versions available.

[Additional details about androidx.activity:activity-compose](androidx_activity_activity-compose.md.html).
(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("NoCollectCallFound")
  fun method() {
     PredictiveBackHandler(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("NoCollectCallFound")
  void method() {
     PredictiveBackHandler(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection NoCollectCallFound
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="NoCollectCallFound" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'NoCollectCallFound'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore NoCollectCallFound ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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